Carbon nanotubes (CNTs) are nanomaterials with a wide range of electronic, optical, mechanical, and biological applications. In order to use CNTs as biomaterials, a certain set of the physical, chemical and biological properties of CNTs needs to be satisfied. CNTs are intrinsically insoluble in aqueous solution and extensively bundled. Since biological systems are fundamentally composed of water-soluble molecules and structures, the solubilization of CNTs in aqueous solution is a prerequisite for their use in bioapplications. In addition, surface functionalization of CNTs with biologically active molecules is important in order to give them the capacity to execute specific biological functions.
The two main approaches for the solubilization of CNTs are based on covalent and non-covalent functionalization. In covalent functionalization, functional groups such as carboxylic acids or amines are formed by chemical reactions in defect sites of CNTs, which can then be used as sites for conjugation reactions with bioactive molecules. The problem with this approach is that it can damage the intrinsic structural and electrical properties of pristine CNTs. In contrast, the non-covalent approach can potentially preserve the π-conjugated system of the CNTs. This approach usually uses amphiphilic molecules, in which the hydrophobic part of the molecule wraps around the wall of the CNTs and hydrophilic part interacts with the aqueous solution. Various types of molecule, including low-molecular-weight amphiphiles or surfactants, polymers, and carbohydrates have been used for the non-covalent functionalization and solubilization of CNTs.
Korean Patent Publication No. 10-2004-0075620 describes non-covalent functionalization of carbon nanotubes in the state of solids to form carbon nanotube/nucleic acid complexes. Korean Patent Registration No. 10-0682381 describes carbon nanotube derivatives in which carbon nanotubes are non-covalently functionalized with egg white protein.